Light emitting diode (led) test apparatus and method of manufacture

ABSTRACT

Embodiments relate to functional test methods useful for fabricating products containing Light Emitting Diode (LED) structures. In particular, LED arrays are functionally tested by injecting current via a displacement current coupling device using a field plate comprising of an electrode and insulator placed in close proximity to the LED array. A controlled voltage waveform is then applied to the field plate electrode to excite the LED devices in parallel for high-throughput. A camera records the individual light emission resulting from the electrical excitation to yield a function test of a plurality of LED devices. Changing the voltage conditions can excite the LEDs at differing current density levels to functionally measure external quantum efficiency and other important device functional parameters. Spectral filtering is used to improve measurement contrast and LED defect detection. External light irradiation is used to excite the LED array and improve onset of charge injection light emission and throughput.

This application is a nonprovisional of U.S. Patent Application No.62/522,576 filed Jun. 20, 2017, the contents of which are incorporatedby reference herein.

FIELD OF INVENTION

The present invention relates to light emitting diode (LED) devices.More particularly, embodiments of the invention relate to techniques,including methods and apparatus to functionally test a Light EmittingDiode (LED) array structure during the manufacturing process. In anexample, the method is useful in general LED device functional testingand is particularly useful for functionally testing micro-LED (uLED)devices that can be as small as a few microns on a side. Micro-LEDs aregrown on a support substrate utilizing techniques such asMetallo-Organic Chemical Vapor Deposition (MOCVD) among others. Beforethe individual devices are used in their final lighting or displayapplication, it is desirable to test the LED devices to achieve one ormore of the following: yield evaluation, binning, devicerepair/correction and collecting data for use in manufacturing processfeedback/feedforward.

BACKGROUND OF INVENTION

Light emitting diodes (LEDs) have been used as a replacement technologyfor conventional light sources. For example, LEDs are found in signage,traffic signals, automotive tail lights, mobile electronics displays,and televisions. Various benefits of LEDs compared to traditionallighting sources may include increased efficiency, longer lifespan,variable emission spectra, and the ability to be integrated with variousform factors.

Although highly successful, improved techniques for manufacturing LEDsis highly desired.

SUMMARY

During the LED manufacturing process, LED structures are formed on asubstrate using mass-production processes like those utilized by thesemiconductor industry. Process steps such as cleaning, deposition,lithography, etching and metallization are used to form the basic LEDstructure. To achieve mass-production scale manufacturing and lowercost, numerous devices are simultaneously formed on a substrate usingthese processes. Different substrates and materials are used dependingon the type of LED desired. For example, UV-emitting LEDs are typicallymade from Gallium Nitride (GaN) material that have usually been either aheteroepitaxial layer on sapphire or free-standing GaN substrates madeusing Hydride Vapor Phase Epitaxy (HVPE) or ammonothermal methods. Forother colors, GaAs or GaP substrates can be used. Recently, GaN, GaAs orother III-V semiconductor materials layer-transferred onto a supportsubstrate has become available as another starting substrate type. Otherpossible LED structures that can be tested using methods disclosed inthis invention are organic LED (OLED) device structures fabricated onplastic, glass or other suitable substrates.

Within the LED structure formation manufacturing process, variousoptical and other metrology tests are made to confirm quality andrepeatability. Once the LED structure formation has been completed, itis desirable to perform a functional test of each LED device before thedevice is mounted for use as a LED emitter within a package or as an LEDemitter within a display. Even if there is a common contact to alldevices (i.e. all cathodes are tied together), each individual anode ofeach device would still require individual contact in order tofunctionally test its opto-electronic characteristics. The device sizeand sheer volume of individual LED devices on a substrate makes this achallenging task. For example, a 6″ substrate with LED devices measuring250 μm on a side (typical of general lighting type LEDs) would containover 250,000 devices, each requiring a contact probe/measurement cycle.If the 6″ substrate contained micro-LED device structures of 20 μm on aside, there would be a need to contact each of the more than 40 milliondevices present on the substrate. There is therefore a need to developmethods that allows functional LED device testing without individualcontact.

Embodiments of the invention utilizes a non-direct electrical contactapproach where the current is injected through a capacitor formed usinga dielectric-coated field plate driven by a suitable voltage waveformsource. The other side of the dielectric surface forms a capacitorplaced in proximity to the plane of the individual LED contacts andspecific voltage waveforms are driven between the field plate electrodeand a common LED contact or a second capacitively-coupled LED contact.In a preferred embodiment, a voltage ramp drives the electrodes toforward bias the LEDs situated between these electrodes, developing adisplacement current that flows current into each of the large pluralityof LED devices in a parallel fashion. The functional response (lightemission) is then measured using an integrating camera disposed eitherabove the field plate or below the LED support substrate depending onthe embodiment. Image capture and processing can then extract manyfunctional device tests in parallel. In this manner, as few as twoelectrical contacts could functionally test LED devices numbering in themillions.

After each measurement, the capacitive field plate and other couplingcapacitance elements must be reset or in a manner that would not damagethe LED devices through excessive reverse bias voltage. A suitably slownegative voltage ramp would allow the LED device's minimum leakagecurrent to safely discharge the field plate capacitor without developingdamaging reverse bias conditions. Another measurement cycle can then berepeated.

Changing the forward bias drive voltage ramp would drive differingforward bias current density (A/cm²) into the LED devices, therebyallowing more complex functional test evaluations to be conducted.Device characterization data such as external quantum efficiency as afunction of forward bias current density made possible by selectingdifferent drive voltage waveforms are another feature of this invention.By modifying the field plate dielectric design and voltage ramp values,accurate current injection emission responses of a large plurality ofdevices can be detected over a large current density from about 0.001 to10 or more A/cm2.

One benefit afforded by this functional test method is the eliminationof high-pin count probe cards and probe needles that contact eachaddressable LED device under test. When such probe cards are used, eachLED device is contacted using one or more needle probe pins thatachieves electrical contact on a contact area by pressure and lateralmotion of the sharp metallic pin. This process almost always producescontact pad scratches that can lower LED device yield and reliability.Test reliability, fabrication and maintenance costs of using probe pincards having hundreds or even thousands of probe pins are also ofconcern. Elimination of probe card scratches or marks, increasing LEDdevice yield and reliability and avoiding the use of expensive andfailure-prone high-pin count probe cards is a key benefit of thisinvention.

Yet another benefit of afforded by this functional test method is theability to functionally test within the LED manufacturing process due tothe elimination of direct electrical contact. Clean-room compatible,scratch-free in-process testing of LED devices is a capability thatwould have otherwise being difficult or impractical to perform due tothe necessity of high-density particle generating pin cards use byconventional test methods.

Other benefits afforded by this functional test method is its generalapplicability to both small and large LED devices and scalability tolarge substrates. The field plate is a structure that appliescapacitance proportionally to area and thus, larger LED devices withmore area are excited with a larger effective capacitance while smallLED devices such as micro-LED devices are excited by a correspondinglysmaller capacitance. Large LEDs of millimeter size on a side down tomicro-LEDs as small as 10 μm or less on a side can therefore be testedwith few modifications of the apparatus. Substrate scalability usinglarger field plates or using a step/repeat method with a smaller fieldplate is practical and readily achievable. For the highest throughput,parallel processing of multiple cameras arranged in an array over alarge field plate would be able to functionally test all LED devices ona support substrate with as few as two electrical contacts and in someembodiments, with no direct electrical contact. Avoiding contacting eachindividual LED device that could number from many thousands to tens ofmillions on a substrate is a key benefit of this invention.

The method as described in this invention is described as CapacitiveCurrent Injection (C²I) functional testing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified cross-section of an LED structure.

FIG. 2 shows an LED support substrate containing LED device structureswithin an LED mass-production process.

FIGS. 3A-B shows a top view (A) and a cross-sectional view (B) of a LEDsupport substrate with singulated LED devices isolated by streets.

FIG. 4 shows the LED support substrate with a non-singulated LED devicestructure with the top contact layer having sufficiently high sheetresistance to allow current injection functional test in the presence ofadjacent shorts.

FIG. 5A shows an embodiment of a field plate in close proximity to aportion of an LED device layer containing 4 LED devices on a supportsubstrate.

FIG. 5B shows the corresponding equivalent electrical circuit of theembodiment of FIG. 5A.

FIG. 6A shows the main Capacitive Current Injection (C²I) measurementsequence: Current Injection/Measurement (I), Hold (II), Discharge/Reset(III) phases.

FIG. 6B shows the corresponding LED current injected by the CapacitiveCurrent Injection (C²I) measurement sequence of FIG. 6A.

FIGS. 7A-B shows two embodiments of a field plate with camera lookingthrough the field plate (A) and through the LED device support substrate(B).

FIG. 8 shows the expected current density (A/cm2) versus dV/dT voltageramp of a preferred embodiment.

FIG. 9A shows a substrate scale method to attach the field plate onto asupport substrate containing LED device structures using vacuumdeveloped in the space between the field plate and the supportsubstrate.

FIG. 9B shows a substrate scale method to attach the field plate onto asupport substrate containing LED device structures using a liquid gappresent in the space between the field plate and the support substrate.

FIG. 10 show a smaller field plate & camera optical system in astep/repeat mechanical configuration.

FIG. 11 show a circuit model used to simulate the C²I functional testmethod according to an embodiment.

FIGS. 12A-D show the detailed sequence of the currentinjection/measurement phase I of an embodiment.

FIGS. 13A-D show the detailed sequence of the currentinjection/measurement phase III of an embodiment.

FIGS. 14 A-D shows a longer time axis (200 msec) showing 4 measurementsequences of an embodiment.

FIG. 15A shows an embodiment of a field plate in close proximity to aportion of a LED device layer containing 4 LED devices on a supportsubstrate with a buried common contact and dielectric layer.

FIG. 15B shows the corresponding equivalent electrical circuit of theembodiment of FIG. 15A.

FIG. 16 shows an embodiment of a field plate in close proximity to aportion of a LED device layer containing 4 LED devices on a supportsubstrate that is used as a dielectric layer for capacitively couplingthe second electrode.

FIG. 17 shows three LED structures A, B and C in which structure A is avertical LED structure with top surface area accessing the top contactby top capacitive coupling and the bottom surface area accessing thebottom contact by bottom capacitive coupling, structure B is a lateralMESA-type LED structure with top surface area accessing both the topcontact and bottom contact by top capacitive coupling and the bottomsurface area accessing the bottom contact by bottom capacitive coupling,and structure C is a lateral MESA-type LED structure with a small topvia opening to the bottom contact. Except for differing relativecapacitance values, structure C is electrically similar to structure B.

FIG. 18 shows three capacitive coupling configurations A, B and C, whereconfiguration A uses a common top field plate electrode, configuration Buses a patterned top field plate electrode only coupling to the top(anode) contact, and configuration C uses a patterned top field plateelectrode with separate top (anode) and bottom (cathode) contacts.

FIG. 19 shows a charge injection response transfer functiondemonstrating the LED bias precharge effect using external light sourceirradiation prior to C²I charge injection.

FIG. 20A shows a representative UV-IR cutoff imaging filter transmissioncurve used in a specific embodiment.

FIG. 20B shows a representative bandpass imaging filter transmissioncurve used in a specific embodiment.

FIG. 21 shows a histogram plot of several LED devices falling withinsmall ranges of Data_(n) values (called channels or bins) on thevertical scale as a function of Data_(n) in the horizontal scale.

DETAILED DESCRIPTION

A further explanation of LEDs is found throughout the presentspecification and more particularly below. In an example, one type ofLED is an organic light emitting diode (OLED) in which the emissivelayer of the diode is formed of an organic compound. One advantage ofOLEDs is the ability to print the organic emissive layer on flexiblesubstrates. OLEDs have been integrated into thin, flexible displays andare often used to make the displays for portable electronic devices suchas cell phones and digital cameras.

Another type of LED is a semiconductor-based LED in which the emissivelayer of the diode includes one or more semiconductor-based quantum welllayers sandwiched between thicker semiconductor-based cladding layers.Some advantages of semiconductor-based LEDs compared to OLEDs caninclude increased efficiency and longer lifespan. High luminousefficacy, expressed in lumens per watt (lm/W), is one of the mainadvantages of semiconductor-based LED lighting, allowing lower energy orpower usage compared to other light sources. Luminance (brightness) isthe amount of light emitted per unit area of the light source in a givendirection and is measured in candela per square meter (cd/m²) and isalso commonly referred to as a Nit (nit). Luminance increases withincreasing operating current, yet the luminous efficacy is dependent onthe current density (A/cm²), increasing initially as current densityincreases, reaching a maximum and then decreasing due to a phenomenonknown as “efficiency droop.” Many factors contribute to the luminousefficacy of an LED device, including the ability to internally generatephotons, known as internal quantum efficiency (IQE). Internal quantumefficiency is a function of the quality and structure of the LED device.External quantum efficiency (EQE) is defined as the number of photonsemitted divided by the number of electrons injected. EQE is a functionof IQE and the light extraction efficiency of the LED device. At lowoperating current density (also called injection current density, orforward current density) the IQE and EQE of an LED device initiallyincreases as operating current density is increased, then begins to tailoff as the operating current density is increased in the phenomenonknown as the efficiency droop. At low current density, the efficiency islow due to the strong effect of defects or other processes by whichelectrons and holes recombine without the generation of light, callednon-radiative recombination. As those defects become saturated radiativerecombination dominates and efficiency increases. An “efficiency droop”or gradual decrease in efficiency begins as the injection-currentdensity surpasses a low value, typically between 1.0 and 10 A/cm².

Semiconductor-based LEDs are commonly found in a variety ofapplications, including low-power LEDs used as indicators and signage,medium-power LEDs such as for light panels and automotive tail lights,and high-power LEDs such as for solid-state lighting and liquid crystaldisplay (LCD) backlighting. In one application, high-poweredsemiconductor-based LED lighting devices may commonly operate at400-1,500 mA, and may exhibit a luminance of greater than 1,000,000cd/m². High-powered semiconductor-based LED lighting devices typicallyoperate at current densities well to the right of peak efficiency on theefficiency curve characteristic of the LED device. Low-poweredsemiconductor-based LED indicator and signage applications often exhibita luminance of approximately 100 cd/m² at operating currents ofapproximately 20-100 mA. Low-powered semiconductor-based LED lightingdevices typically operate at current densities at or to the right of thepeak efficiency on the efficiency curve characteristic of the LEDdevice. To provide increased light emission, LED die sizes have beenincreased, with a 1 mm² die becoming a fairly common size. Larger LEDdie sizes can result in reduced current density, which in turn may allowfor use of higher currents from hundreds of mA to more than an ampere,thereby lessening the effect of the efficiency droop associated with theLED die at these higher currents.

LEDs have been used in portable devices such as watches, smartphones andlaptops as well as computer monitors and TV displays for many yearshowever only indirectly as an alternative white light source forLiquid-Crystal Display (LCD) display technologies. These were called“LED” TVs and the like, but the actual LEDs were predominantly GaN-basedwhite LEDs to illuminate the backlight in lieu of the cold fluorescentlamp (CFL) backlight sources used before. The color pixel generationcontinued to be based on LCD technology that worked by a lightsubtraction process where colors are generated by blocking other colorsusing an intervening color filter. For example, a red pixel would begenerated by a red color filter that blocked the green and blue portionof the backlight LED white spectrum. Grey scale (light intensity of thepixel) occurred by modulating light polarization through aliquid-crystal cell placed between two crossed polarizers along thelight path.

Although the LED backlight driven LCD display technology was moreefficient and reliable than the CFL backlit version, the technology isstill not power efficient. The reason is simple: although the LED whitebacklight devices can be fairly efficient in terms of external quantumefficiency (photons emitted per electrical carriers injected into theLED device), there are numerous inefficiencies in the rest of this LCDdisplay technology. The first polarizer will cut a little half of thenon-polarized white backlight, then each pixel is colorized bysubtracting ⅔ of the remaining light (R without GB for red, G without RBfor green and B without RG for blue). Other losses include pixel fillfactor and film/LCD cell absorption and scattering. The total lightoutput is therefore less than about ⅙ of the white LED backlightintensity.

The trend is for more power efficient and bright display technologies,especially with portable, battery operated devices where battery life isa key factor. Micro-LED is a promising technology for achieving higherpower efficiencies. In a micro-LED display, a small LED device placedwithin a pixel area is directly driven to generate light in a directemissive manner. Color can be generated either by (i) utilizing blue toUV-LEDs (i.e. GaN-based) with color phosphors or quantum-dot colorconversion layers to generate the pixel colors by photon down conversionand/or (ii) by using LEDs that generate the color directly (i.e. AlGaAs,GaAsP, AlGaInP, GaP for red, GaP, AlGaInP, AlGaP for green and ZnSe,InGaN, SiC for blue). In either case, the direct emission/direct view ofthe micro-LED display promises a six-fold improvement or more in powerefficiency.

Although the basic technology to realize micro-LED based displays iswell known, numerous manufacturing and quality control challenges exist.One of these is functionally testing millions of micro-LED deviceswithin the manufacturing process in a cost-effective and efficientmanner before the pixels are committed to use. It is therefore desiredto enable functional testing without direct electrical contact and in amanner compatible with micro-LED large-scale manufacturing processes.Further details of the present invention can be found throughout thepresent specification and more particularly below.

Embodiments of the present invention describe LED device fabricationprocesses and manners of functionally testing LED devices without directelectrical contact. In particular, some embodiments of the presentinvention may relate to manners of functionally testing high-brightnessLED, medium power LED, low-power LED and micro LED devices.

In various embodiments, description is made with reference to figures.However, certain embodiments may be practiced without one or more ofthese specific details, or in combination with other known methods andconfigurations. In the following description, numerous specific detailsare set forth, such as specific configurations, dimensions, andprocesses, etc., in order to provide a thorough understanding of thepresent invention. In other instances, well-known semiconductorprocesses and manufacturing techniques have not been described inparticular detail in order to not unnecessarily obscure the presentinvention. Reference throughout this specification to “one embodiment”means that a feature, structure, configuration, or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the invention. Thus, the appearances of the phrase “in oneembodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the invention.Furthermore, the features, structures, configurations, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

The terms “spanning”, “over”, “to”, “between” and “on” as used hereinmay refer to a relative position of one layer with respect to otherlayers. One layer “spanning,” “over” or “on” another layer or bonded“to” or in “contact” with another layer may be directly in contact withthe other layer or may have one or more intervening layers. One layer“between” layers may be directly in contact with the layers or may haveone or more intervening layers.

Certain embodiments of the invention describe an LED device assembly inwhich an LED device structure layer is transferred from a supportsubstrate and bonded to a pickup plate assembly before furtherprocessing. In accordance with embodiments of the present invention, theC²I functional testing step can be applied either before the transfer orafter one or more transfers. For the purposes of simplifying the variouspossible configurations wherein the plurality of the LED structures istransferred and possibly bonded onto a different substrate, the targetsubstrate shall be called a support substrate in each case. For example,the substrate that supported the LED structures during MOCVD growth isalso called a support substrate, however after release and attachment toa pickup plate, such a plate and any other substrate or plate used tomechanically support the LED device layer will also be called a supportsubstrate. If a pickup plate is used, common electrical contact can beaccomplished using an electrically conducting material film between thetransferred LED device structures and the rest of the pickup plate. Asfurther described below, the common contact can also be accomplishedusing a second dielectric layer and optional voltage waveform source. Insome cases, the pickup plate material would also have a degree ofcontrollable tackiness to allow LED device pickup and transfer inproduction. Additionally, the support substrate can be a flexible sheetsuch as a plastic film and the C²I can be used to test device structureson individual sheets or as part of a roll-to-roll manufacturing process(for example in an Organic-LED or OLED manufacturing process). The termsupport substrate will be generally used to connotate its role asmechanical support and will be the substrate described as part of (C²I)functional testing apparatus throughout this description.

Although the embodiments of this invention describe singulated andnon-singulated LED device structures, additional electronics such asactive-matrix addressing circuitry and support electronics can bepresent. Applying design for testability approaches and using thegeneral ability of the C²I functional test methods could successfullytest complex interconnected LED structures. For purposes of thisinvention, specific descriptions of the LED structures shall be taken asmerely examples and the test methods is to be understood as generallyapplicable to test singulated, non-singulated, lateral and vertical LEDstructures with or without integrated addressing and other supportelectronics.

Depending on the specific embodiment of this invention and the point inthe manufacturing process C²I functional testing is made, the supportsubstrate can be transparent and have additional coatings. These eitherdirectly support the test process or exist as part of the requirementsof the specific LED manufacturing process step as will be described inmore detail below.

Referring to FIG. 1, a representative LED 104 comprises of depositedlayers that form a n-type cathode layer 100, an active layer (usually aMulti-Quantum Well or MQW series of sub-layers) 101 and a p-type layer102 and p-contact 103. This LED structure is simplified and manyadditional layers such a buffer layers, blocking layers, n-contactlayer(s) and the like are not shown for simplicity. Electrically, theLED would be contacted through layer 103 (or contact 106) as the anodeand through layer 100 (or contact 105) as the cathode. In some LEDstructures, the n and p layers can also be contact layers and thus canbe named interchangeably for purposes of this invention unlessspecifically described otherwise. Passing current through the LED deviceusing a forward (positive voltage) bias from anode to cathode wouldgenerate light from radiative recombination processes from carriersflowing through the active region. The design of the active layer 101 isoptimized for maximizing radiative recombination processes that emitlight. Reverse biasing the LED structure will not generate light.Limiting reverse bias voltage is important with LEDs to avoid damagingor destroying the device through a process called breakdown. Within asafe reverse bias region, small leakage currents flow through thedevice.

In LED manufacturing, the LED devices are made in mass-production usingmethods similar to substrate-based mass-production processes common inthe semiconductor industry. Referring to FIG. 2, the LED structuredescribed in FIG. 1 is deposited onto a suitable growth or supportsubstrate 201 to make an LED substrate 200. Depending on the type,quality and color of the LED desired, different substrate material typescan be used. Examples are GaP, GaAs, GaN substrates or heteroepitaxialgrowth substrates such as sapphire and silicon carbide (SiC) are alsopossible. Layer-transferred semiconductor layered template substratesare yet another type of growth substrate. The LED structure is thengrowth to develop a lower contact 202 (n-type or cathode in thisexample), active region 203 and upper contact 204 (p-type or anode inthis example).

The LED substrate of FIG. 2 contains multiple, non-singulated LEDstructures. Isolation of individual LED devices of the desired size andfunction can be made within the LED manufacturing sequence using processsteps such as etching, lithography, passivation and deposition.Referring to FIGS. 3A and 3B, the desired LED devices can be isolatedwhile residing on support substrate 301 using processes such as etchingto form for example a trench 308. If these etch structures (sometimescalled “streets”) are made over the substrate to form individuallyisolated structures such as square devices, a high number of LED devices309 are electrically isolated and available for release and packaging.In this example, the trench 308 does not etch through the bottom commoncontact layer 302 and can thus be connected to a common potential 310.Each LED device 309 can thus be individually contacted using a voltagesource 306 to the p-layer 304 and p-contact layer 305. Light 307 canthen be measured from the contacted device to evaluate itsfunctionality. In this example, a top emitting LED structure is shownwhere the top contact 305 could be a transparent electrode such asIndium Tin Oxide (ITO). Other structures are possible such as a bottomemitting structure. In this case, the support structure would bepreferably transparent and the p-contact layer would be a lightreflecting layer such as a metal layer. The LED would thus be tested bymeasuring the light escaping from the support substrate. Although theabove was described as preferred embodiments to maximize the lightcapture, it would be possible to measure indirectly scattered orreflected light from LEDs even if the light measurement was done, forexample, above the LED in a bottom emitting LED structure. Of course,there can be other variations, modifications, and alternatives.

FIG. 4 shows a support substrate 401 where the LED devices are still notisolated. If the top contact layer 405 has a limited conductivity (suchas an ITO layer with a relatively high film sheet resistivity),functional testing could still be accomplished despite a short 408present nearby. Contacting a point on the surface using a voltage source406 would develop a current through the top contact 405, p-layer 404,active layer 403, n-layer 403 to common contact 402. The relatively highresistance to the neighboring short 408 could allow light emission 407to occur. Using a field plate in lieu of this direct contact exampleaccording to an embodiment of this invention would allow non-singulatedLED layer testing. Dark (non-emissive) or weakly emissive areas would bean indicator of LED layer functional yield at an early stage of the LEDmanufacturing process. The efficacy and spatial resolution of thisalternative embodiment would be a function of top layer sheetresistivity.

There is therefore a need to inject a current to excite individual LEDdevices or LED areas such as described in FIGS. 3 & 4 in a manner thatcan support large-scale manufacturing.

In a preferred embodiment, the invention has as its current injectiondevice a field plate comprising of 3 elements: a mechanical supportplate, an electrode and a dielectric layer. Referring to FIG. 5A, thefield plate 501 comprises of a field plate support (top), electrodelayer 502 connected to a voltage source 503 and adjacent to one face ofdielectric layer 504. The mechanical support plate can also beelectrically conductive and only require a dielectric layer.

The invention is primarily described with a physical dielectric layer104 such as an oxide or other insulator such as a polymer or plasticoverlying the electrode layer 502 but this is not necessary. Desiredcharge injection can also be made to occur if a suitable gap medium isselected between the electrode layer 502 and the device contact layer508. In such embodiments, care in biasing should be taken to avoidunwanted resistive shorts or dielectric breakdown within the gap medium.In numerous succeeding examples, the field plate dielectric and a gapdielectric is described, sometimes with the gap layer assumed to have asufficiently high capacitance to have a negligible effect on theeffective system coupling capacitance. The combination of interveningregion(s) between the field plate conductive layer and thelight-emitting diode structure is also called the interface region. Itis to be understood that the effective field plate coupling capacitancecan also consist of a gap medium with or without a field platedielectric layer. Of course, there can be other variations,modifications, and alternatives.

The field plate electrode would be connected to voltage source 503 andthe open face of the dielectric layer 504 would form a capacitance perunit area of:

C′ _(FP)=ε_(o×)ε_(r) /t _(d)   (1)

-   Where-   C′_(FP) is the capacitance per unit area of the field plate (F/cm²)-   ε_(o) is vacuum permittivity (8.854×10⁻¹⁴ F/cm)-   ε_(r) is the relative permittivity of the dielectric layer    (dimensionless)-   t_(d) is the dielectric layer thickness (cm)    In an example, important material characteristics of the dielectric    layer material includes dielectric constant, dielectric breakdown    strength, resistivity, and optical transmissivity. For capacitive    coupled configurations, readily deposited dielectrics such as    silicon dioxide, silicon nitride and alumina (Al₂O₃) are of    particular interest. If a DC test configuration is desired, a    dielectric having limited current leakage would allow DC biasing if    coupled to the device using an appropriate gap medium also having    limited resistivity. In such a configuration, the field plate    dielectric can be optional where the field plate voltage can now be    directly coupled to the LED devices through the gap medium. Of    course, there can be other variations, modifications, and    alternatives.

Again referring to FIG. 5A, the field plate 501 would be placedsufficiently near LED support structure 505 with an n-contact bottomelectrode 506 connected to a common contact 507 and a plurality ofp-contact top electrodes 508. Although the voltage across each LEDdevice is shown in this description as being developed using a voltagesource 503 and common contact 507, the voltage source can bealternatively connected to the bottom or two voltage sources can beconnected, one to each of electrodes 502 and 506. The effective LEDdevice drive voltage would be the voltage difference between contacts503 and 507 for all voltage source configurations. For this invention,the term “close proximity” shall mean the open face of the field platedielectric layer 504 is placed in sufficient proximity to the open faceof the LED structure contact surface 508 to allow a desired electricalcoupling between the voltage source 503 to the top LED electrode surface508. In FIG. 5A, this gap is shown as 509 and can be minimal with alimited gap or no gap. Gap 509 should be small enough to allowsufficient capacitive coupling (for optimizing the current injectionefficiency) and to minimize spatially defocusing the current injectioneffect. For top plate 501 with a relatively thick dielectric layer 504and higher voltage levels on voltage source 503, a limited gap 509 ispossible to allow non-contact testing without significantly loweringcoupling efficiency (C_(EFF)′˜C_(FP)′).

The electrical analogue of the structure made by assembly 500 is shownin FIG. 5B. Voltage source 510 (503 in FIG. 5A) is connected to aneffective capacitor C_(EFF) 511 connected to LED device 512 having a topsurface area A_(EFF). A voltage change will impress a current I_(LED)onto LED device 512. For this example, isolation of LED devices with acommon bottom contact is assumed. The effective capacitance C_(EFF) issimply the series capacitance of the field plate dielectric layer withthe capacitance of gap 509, both of area A_(EFF):

C′ _(gap)=ε_(o×)ε_(r) /t _(gap)   (2)

-   Where-   C′_(gap) is the capacitance per unit area of the gap (F/cm²)-   ε_(o) is vacuum permittivity (8.854×10⁻¹⁴ F/cm)-   ε_(r) is the relative permittivity of the gap medium (dimensionless)-   t_(gap) is the gap thickness (cm)-   and

C _(EFF) =A _(EFF)×(C′ _(FP) ×C′ _(gap))/(C′ _(FP) +C′ _(gap))   (3)

C _(EFF)=(C′ _(FP) ×C′ _(gap))/(C′ _(FP) +C′ _(gap))   (4)

-   Where-   C_(EFF) is the effective LED device coupling capacitance (F)-   C′_(EFF) is the effective LED device coupling capacitance per unit    area (F/cm²)-   A_(EFF) is the effective LED device area (cm²)

In yet other embodiments, the field plate is without a field platedielectric layer 504 between the field plate electrode 502 and the LEDdevice under test top contact 508. The gap material would serve as thedielectric material. Although a vacuum or air gap is less cumbersomethan a liquid, the lower relative dielectric constant (roughly unity) ofthese mediums can capacitively couple less efficiently and become weaklyionized or even breakdown under sufficiently high bias conditions. Ifthe gap material is of a suitably high dielectric constant, dielectricstrength and resistivity, efficient coupling of the field platepotential can help improve capacitive coupling efficiency. For example,deionized (DI) water may be a good candidate liquid material to serve asa gap dielectric. With a high relative dielectric constant of DI water(ε_(r)˜81) and breakdown electric field of about 13 MV/m, a DI waterfilled gap layer can efficiently inject charge per unit area withoutbreaking down. Bulk resistivity of pure to ultra-pure DI water rangeabout 1-18 Megohm-cm. Type II DI water (>1 Megohm-cm) may be sufficientto serve as a gap dielectric without excessive injected bias relaxationif the gap parameters (i.e. thickness) and injection and measurementtiming are appropriately selected.

If a liquid is selected as a gap medium, DI water is also industriallydesirable due to its low cost, broad availability, materialscompatibility and cleanliness compared to other possible liquids such asmethanol and ethylene glycol.

For the next embodiments, C′_(EFF) will be made equal to C′_(FP) by afield plate dielectric layer coupled to the LED device via asufficiently small gap 509 and/or using a gap medium with a highrelative dielectric constant.

The current I_(LED) 513 and current density J_(LED) are readilycalculated as:

I _(LED) =C _(EFF) ×dV/dt   (5)

J _(LED) =C′ _(EFF) ×dV/dt   (6)

Where dV/dt is the voltage rate of change between the voltage source 510and the common electrode 507 in FIG. 5A (or the cathode contact in FIG.5B). For this particular embodiment, LED 512 is connected anode tocathode however cathode to anode injection is possible by reversing allvoltage polarities.

FIGS. 6A and 6B shows the voltage and current waveforms that would forma measurement sequence according to a preferred embodiment of thisinvention. There are at least 2 phases in the measurement sequence, thecurrent injection phase I (at time t₀ to t₁) and the discharge phase III(at time t₂ to t₃). A voltage holding phase II has been added to allowfor enough time for the camera integration window to close before phaseIII commences however this can be very short and may not be necessary.The phases are described in more detail below and assumes null voltageat all point before t₀.

Referring to FIG. 6A, a voltage source-time plot 600 shows the voltagesource waveform. At time t₀, phase I begins with a positive ramp dV/dt|₁from 0 to V₁ from time t₀ to t₁. This ramp will inject a current I_(LED)into a LED of area A_(EFF) according to equation (5) and a correspondingcurrent density J_(LED) according to equation 6. At time t₁, the voltageis held at this voltage V₁ until time t₂. From time t₂ to t₃, thevoltage is lowered back to a zero-voltage state using a negative rampdV/dt|₂. At time t₃, another measurement sequence can then commence.

FIG. 6B shows the corresponding current I_(LED) waveform during themeasurement sequence from the driving waveform of FIG. 6A. During phaseI, a near constant I_(LED) current will flow through the LED deviceaccording to equation (5). Light 602 will be emitted during Phase I.During Phase II, I_(LED) and light emission will drop to 0. To measurethe light output of a particular LED device among a plurality of devicessimultaneously being excited by the field plate, an integrating camerathat can capture the light from one or more LED devices is used. Imageprocessing can generate a value proportional to specific LED deviceslocated within the camera's field of view. This value would be in turnproportional to the optical energy integrated over phase I. It istherefore desirable to start an image sensor integrating time periodfrom a point slightly before t₀ to an end point slightly after t₁. Thiswill ensure the camera integrating sensor will capture the completelight pulse emanating from the LED structures during phase I.

FIGS. 7A and 7B shows two embodiments of the invention. The figures showtop and bottom camera placement that can intercept at least a portion ofthe plurality of LED devices being excited by the measurement sequencethrough the field plate. Referring to FIG. 7A, a test configuration 700is shown with a transparent field plate assembly 702 including a fieldplate electrode 703 and dielectric layer 704. Electrode 703 is connectedto a voltage source 705. This assembly is placed in close proximity tothe LED device support substrate 701 supporting a plurality of LEDdevice 707 connected to a common contact 706. A camera 708 is placedabove the field plate assembly 702 to perform the functional test. FIG.7B shows an alternative test configuration 709 where the camera isplaced below the support substrate. In this configuration, the supportsubstrate and intermediate layers to the LED device structures must betransparent to allow the light to reach the camera.

Optical power generated by an LED is related to electrical power flowingthrough the LED by the external quantum efficiency η_(EXT) orP_(opt)=η_(EXT)×P_(elec). The parameter η_(EXT) is in turn quitesensitive to the current density and other device characteristics suchas light extraction efficiency. The optical power of an LED device isthus related to electrical power as:

P _(opt)=η_(EXP) ×P _(elec)=η_(EXT) ×I _(LED) ×V _(F)=η_(EXT) ×C _(EFF)×dV/dt×V _(F)   (7)

-   Where-   P_(opt)=LED optical power (W)-   η_(EXT)=LED external quantum efficiency-   V_(F)=LED forward voltage drop (V)    Over a time period Δt=t₁−t₀ (phase I):

E _(opt)=η_(EXT) ×C _(EFF) ×dV/dt×V _(F) ×Δt=η _(EXT) ×C _(EFF) ×ΔV×V_(F)=η_(EXT) ×Q _(inj) ×V _(F)   (8)

-   Where-   E_(opt)=LED optical energy emitted during phase 1 (J)-   ΔV=Total voltage change over Δt (V)-   Q_(inj)=Injected charge (Coulombs)

According to equation 8, the integrating camera will measure a valueproportional to each measured LED's external quantum efficiency.Changing the voltage ramp value will have the effect of selecting adifferent current density according to equation 6. By plotting Eopt as afunction of ramp value to V₁, a plot of light energy (related toη_(EXT)) as a function of J_(LED) can be generated. This capability canbe particularly useful to measure low current density performance ofmicro-LED devices. Micro-LED devices are typically driven at very lowvalues of 0.001-1 A/cm² and are more sensitive to drop in externalquantum efficiency at these low levels due to non-radiativerecombination processes.

During phase III, a negative dV/dt ramp allows the voltages to bereturned to zero to reset the system for another measurement. Duringthis phase, the LEDs will be reverse biased and will discharge C_(EFF)using reverse bias leakage current. So as not to reverse bias the LEDsto a voltage level that can cause damage, the negative voltage ramp mustbe sufficiently slow to keep all devices within a safe reverse biasvoltage range. Such a range can be selected depending on the type anddesign of the LEDs to be tested. As merely an example, reverse biasleakage current density for GaInN LEDs can be estimated using a paperentitled “Transport mechanism analysis of the reverse leakage current inGaInN light-emitting diodes”, Q. Shan & al., Applied Physics Letter 99,253506 (2011). FIG. 2 shows a −5V reverse bias leakage current ofapproximately 1.5×10⁻⁷ A on a 1 mm² LED device at room-temperature. Thiscorresponds to 15 μA/cm². This reverse bias leakage current density willbe used to calculate values and parameters for specific C²I examplesdescribed in first examples below. In yet other embodiments that will bedescribed later in this invention, an externally applied light sourcecan increase the available leakage current to safely lower the dischargetime and improve system throughput.

Suitable integrating cameras must satisfy the following criteria:

-   -   a. Pixel sensitivity and dynamic range (allows LEDs to be        accurately measured through the operating range of interest        without excessive dark noise and signal saturation).    -   b. High pixel density and frame rate (increases throughput and        parallel LED measurement).    -   c. Global shutter and flexible triggering (all pixels must be        triggered and integrate over the same time period).        One example of an industrial camera meeting these criteria is        model GS3-U3-23S6M-C from PointGrey Research Inc., Richmond, BC,        Canada. The camera is a 2.3 megapixel (1920×1200) monochromatic        camera with global shutter, 5 μsec to 31.9 sec exposure range,        over 160 frames per second rate, 1/1.2″ sensor format, 12-bit        digitization, 5.86 μm pixel size, 72 dB dynamic range, 76%        quantum efficiency (525 nm), an e-saturation capacity of about        32,000 electrons and temporal dark noise of about 7 e-. Used        singly or in a matrix arrangement where n×m cameras would be        used to measure a larger field plate area simultaneously, the        camera will have the capability to measure numerous LED devices        with the requisite accuracy.

For the following examples, a field plate with a 3 μm silicon dioxidedielectric layer is assumed (ε_(r)=3.9). This dielectric material iscommonly used and can be sputtered, grown or deposited on numerousmaterials. The thickness was selected to be sufficiently thin to supporta voltage exceeding about 1500 volts before breakdown. C′_(FP) would be1.15 nF/cm².

A value for V₁ of 500V is assumed (see FIG. 6A). With these assumptionsand parameter selections, the light pulse energy per LED can besimplified as:

E _(opt)=η_(EXT) ×C _(EFF) ×ΔV×V _(F)   (9)

For the parameters selected, FIG. 9 shows the current density selectedfor a voltage ramp time period. For example, the LED would be driven at0.01 A/cm² if the field plate voltage was driven from zero to +500 Voltsin approximately 60 μsec (phase I). The camera shutter would be openedslightly before the ramp begins (for example, 10-50 μsec before t₀) andwould be opened slightly after the end of phase I (for example, 10-50μsec after t₁). Apart from ensuring that the phase I LED light pulse isfully integrated within the camera shutter time window, excessiveintegration time should be avoided as this will tend to raise the noisefloor of the camera. Phase II can be selected to end just as theintegrating shutter closes.

To safely recover during phase III, equation 6 is utilized with thecurrent density selected to be approximately equal to the leakagecurrent density. For example, utilizing a target leakage current densityof 10 μA/cm² (a little lower than the expected leakage of 15 μA/cm²) andΔV=500V, equation 6 predicts a minimum Δt of almost 60 msec. Thiscorresponds to a measurement repetition rate of about 16 frames perseconds for injection current densities of 0.0005 A/cm² or above.

To estimate the signal achievable with this measurement approach and thearea covered by one camera, the following additional parameters areassumed:

-   -   a. GaN LED (about 410 nm emission & 65% camera quantum        efficiency)    -   b. V_(F) about 3V    -   c. E_(opt)=170 nJ/cm2 (η_(EXT)˜10%)        At about 3 eV per photon, approximately 3.5×10¹¹ photons/cm² are        emitted during phase I. The number of corresponding        photo-electrons that can be generated within the camera would be        0.65×3.5×10¹¹ photons/cm² or 2.3×10¹¹ photo-electrons/cm²        (assuming sensor to field plate 1:1 magnification and 100%        collection efficiency). At this magnification, a 5.86 μm pixel        size would still capture over 78,000 electrons, more than twice        the pixel saturation capacity. A lower V₁ voltage could be        selected if a lower integrated photo-electron count per camera        pixel is desired.

Using a 0.5× collection lens (model #62-911 TECHSPEC™ large formattelecentric lens manufactured by Edmund Optics, Barrington, N.J., USA)as an example, a roughly 21 mm×16 mm LED substrate area will be imagedonto the image sensor, although there can be variations. The workingdistance is 175 mm and the entrance aperture is roughly 90 mm, resultingin about 1.7% total collection efficiency compared to 4π sr. Theexpected photo-electrons collected would be 2.3×10¹¹photo-electrons/cm²×(5.86 μm×2)²×0.017=5.3 ke⁻/pixel. This is wellwithin the sensor's dynamic range and signal averaging or increasing V₁could further improve signal quality if desired. Of course, there can beother variations, modifications, and alternatives.

The imaging of the field plate to the camera sensor area is thus less afunction of the available signal than the number of pixels allocated perLED device. For a larger LED device measuring 250 μm on a side, lessmagnification is necessary. Assuming a 2×2 pixel area to cover each LEDdevice for accurate metrology, one camera could measure 960×600 LEDdevices, 240 mm×150 mm field plate area or more than the area of a 6″support substrate. In this example, V₁ could be reduced to less than100V and perhaps lower while still maintaining excellent signal to noiseratio. If the light pulse energy is too high, a neutral density filteror other absorption filter can be placed between the emitting surfaceand the camera to avoid camera saturation.

For a micro-LED application with 10 μm×10 μm LED device size, the same960×600 LED devices per sensor would be measured or about 9.6 mm×6 mmfield plate area. A step and repeat system with approximately 16×25steps would allow testing of a 6″ micro-LED substrate containing over170 million devices. If a single measurement per LED device issufficient, a synchronized image capture with a moving camera or camerascould decrease test time to less than 1 minute or even a few seconds.For example, a 16 frame per second capture rate would allow a full 6″substrate to be functionally tested in about 25 seconds. That wouldcorrespond to over 9 million LED devices tested per second, far fasterthan probe cards and individual test methods.

In a preferred embodiment, FIG. 9 shows a substrate-sized field platecan be attached to a support substrate using vacuum (FIG. 9A) or aliquid such as DI water (FIG. 9B) to make an assembly 900 or 910suitable for functional test. FIG. 9A shows an example where vacuum isused as a gap medium. The field plate 901 is placed on the LED devicesupport substrate 902 with a compliant vacuum seal 903 placed on theoutside peripheral area to maintain a level of vacuum between the fieldplate and the LED device support substrate. The air is then evacuated inthe space between the plates using vacuum port 904. The plates would bepressed together at up to atmospheric pressure to minimize the gap in auniform manner, thus optimizing the effective field plate couplingcapacitance C_(EFF). A support substrate exchange mechanism couldexchange substrates to be tested under the field plate by cycling port904 between vacuum and vent conditions. A camera 905 that measures abovethe field plate is shown in this embodiment. FIG. 9B shows an examplewhere liquid is used as a gap medium. The field plate 911 is placed onthe LED device support substrate 912 with a compliant seals 913 placedon the outside peripheral area to maintain a level of sealing betweenthe field plate and the LED device support substrate. The air is thenevacuated in the space between the plates and replaced by the liquidmedium using gap liquid fill input port 914 and gap liquid fill outputport 915. A negative pressure can be maintained by adjusting the inputand output fill port parameters. After filling the gap with the liquidmedium, the plates are kept pressed together at up to atmosphericpressure to minimize the gap in a uniform manner, thus optimizing theeffective field plate coupling capacitance C_(EFF). Reversing theprocess with a backfill gas would largely evacuate the liquid. A supportsubstrate exchange mechanism could exchange substrates to be testedunder the field plate by cycling the gas or liquid port(s) between avent/exchange state to a state that allows measurement with the desiredgap medium. These embodiments show a camera 905 or 916 that measuresabove the field plate. Of course, there can be other variations,modifications, and alternatives.

In another embodiment, FIG. 10 shows an assembly comprising of a smallerfield plate 1000 and camera 1001 placed above an LED device supportsubstrate 1002. The field plate/camera assembly is moved in successivemove/measure steps 1003 to measure the complete substrate 1002. Ofcourse, there can be other variations, modifications, and alternatives.

Electrical simulations of the measurements sequence showing the mainphase 1 and 3 waveforms are shown in FIGS. 11-14. The system beingsimulated is as follows:

-   -   1. Field plate: 3 μm silicon dioxide, C′_(EFF)=1.15 nF/cm2    -   2. 10 μm×10 μm LED device size: 1.15 fF C_(EFF), 15 pA reverse        leakage current    -   3. 0.01 A/cm² current density test point    -   4. V₁=500V (60 μsec ramp time to achieve 0.01 A/cm² current        density injection)    -   5. 60 msec measurement repetition rate    -   6. LED device is a standard diode capable of reverse leakage        current of about 10 pA        The program used is a SPICE circuit simulator called Micro-Cap        version 11 from Spectrum Software (Sunnyvale, Calif.). One 10        μm×10 μm LED device was simulated under the above conditions.        FIG. 11 shows the circuit diagram where C_(EFF)=1.15 fF driven        by a voltage generator V2. This generator was programmed to ramp        from 0 to +500V in 60 μsec followed by a 60 msec ramp down from        +500V to 0V. Voltage source V3 is unconnected but was programmed        to show an example of a desired camera shutter window. In this        example, the shutter is opened 10 μsec before phase I and closes        10 μsec after phase I.

FIG. 12A-D shows the Phase 1 waveforms with the voltage source V2 (FIG.12A), LED device forward bias (FIG. 12B), LED device forward current(FIG. 12C) and the camera shutter control signal from voltage source V3(FIG. 12D). Referring to FIG. 12D, the camera integrator shutter opens10 μsec before the start of the voltage (at time +10 μsec on the timeaxis). At time +20 μsec on the time axis, the voltage source starts toramp towards +500V (time t₀). During this phase I until time +80 μsec,the LED device is biased at +10 nA (FIG. 12C) at a forward bias ofapproximately +250 mV (FIG. 12B). This corresponds to 0.01 A/cm² currentdensity as desired. After time +80 μsec, the voltage ramp stops and theLED current drops to zero. At time +90 μsec, the camera shutter closes,completing its integration of the light pulse that was generated duringphase I. The voltage source will now start a slow discharge at a targetleakage current of −10 pA. FIG. 13A-D shows the same voltage and currentpoints during the phase III discharge lasting about 60 msec. FIG. 13Cshows a −10 pA discharge current that allows C_(EFF) to discharge over60 msec from +500V to 0V safely. After the voltage source is returned tozero at about +60 msec, a new measurement sequence is initiated. FIG.14A-D shows a longer time axis (200 msec) showing 4 measurementsequences.

The field plate electrode is connected to voltage source 503 and theopen face of the optional “leaky” dielectric layer 504 form acapacitance per unit area of:

C′ _(FP)=ε_(o×)ε_(r) /t _(d)   (10)

-   Where-   C′_(FP) is the capacitance per unit area of the field plate (F/cm²)-   ε_(o) is vacuum permittivity (8.854×10⁻¹⁴ F/cm)-   ε_(r) is the relative permittivity of the dielectric layer    (dimensionless)-   t_(d) is the dielectric layer thickness (cm)    The dielectric would have a resistivity of ρ_(d), selected to allow    the desired biasing of the LED devices in a DC bias configuration.    The time constant driving the bias response time is    ε_(o)×ε_(r)×ρ_(d). The effective resistance can be calculated as    follows:

R′ _(FP)=ρ_(d) ×t _(d)(ohms-cm²)   (11)

-   Where-   R′_(FP) is the resistance for a unit area of the field plate    (ohms-cm²)-   ρ_(d) is the resistivity of the field plate dielectric layer    (ohm-cm)-   t_(d) is the dielectric layer thickness (cm)    In an example, the leaky dielectric layer can be generally described    as a layer with a reasonably high relative dielectric constant,    resistivity on the order of 1 Mohm-cm or higher and a sufficiently    high dielectric breakdown field strength. Type II DI (deionized)    water meets these criteria with a dielectric constant of 81,    resistivity of 1 Mohm-cm and a breakdown field strength exceeding 13    MV/cm. In other examples, the layer can be a slightly conductive    doped glass/ceramic, plastic or the like. If a small relative    dielectric constant of about 1 is acceptable, an air layer with a    voltage within a gap could become slightly conductive by weak    ionization to accomplish the function of a “leaky” dielectric layer.

Although this invention has been described with a common contactexisting under the LED devices, other current injection configurationsare possible. FIG. 15A shows another embodiment 1500 where an analogueto the field plate 1501 is present within support substrate 1502 belowthe plurality of LED device structures such as LED device 1503. Underthe lowest LED device structure layer (the n-layer in examples describedin this invention), a dielectric layer 1504 and electrode 1505 completesthe support substrate capacitive coupling device. Electrode 1505 isconnected to a voltage source 1506. The field plate is connected to aseparate voltage source 1507 and field plate electrode 1508. In thisexample, a camera 1509 is placed above the field plate to capture thelight emission response of the plurality of LED devices under test. Inthis example, the isolation between devices is shown to be complete,however this method would still function with or without full isolationof the n-layer. FIG. 15B shows the equivalent circuit 1511 of thiscapacitively coupled support substrate configuration. The only change isthe insertion of a second coupling capacitor C_(EFF2) below each LEDdevice cathode. The resulting circuit can be made to operateequivalently and be effective in performing C²I functional test. Forexample, assuming a support substrate dielectric layer 1504 identical todielectric layer 1510 within the field plate, voltage source 1506 drivenidentically but negatively to voltage source 1507 (0 to −500V for source1506 and 0 to +500V for source 1507), the measurement system 1500 wouldperform essentially identically to a common contact support substrateconfiguration.

In yet another embodiment, C²I functional testing could also be appliedto a modification of the test configuration of FIG. 15A that eliminatesthe need for a buried electrode within the support substrate. In thisembodiment, the dielectric property of the support substrate itself isused to inject current through the LED devices. For example, a quartz,sapphire, glass or plastic support substrate could serve as dielectric1504 in FIG. 15A. FIG. 16 shows a specific embodiment 1600 of thisconfiguration. A support substrate 1601 having adequate dielectricproperties and thickness containing a plurality of LED devices on itssurface such as LED device 1602 is placed on top of an electrode 1603connected to a voltage source 1606. Although not shown specifically, agap can exist between electrode 1603 and support substrate 1601,allowing non-contact operation of the back side of the support substrateif desired. Although not shown specifically, an additional dielectriccan also be interposed between electrode 1603 and support substrate1601. The gap (and optional dielectric covering electrode 1603) willmodify C_(EFF2) in a similar manner as the top field plate to device gap509 modified C_(EFF) & C_(EFF)′ using equations 2-4. Field plate 1604having a dielectric layer 1605 and electrode 1606 connected to a secondvoltage source 1607 completes the C²I functional test circuit. A camera1608 placed above field plate 1604 is shown in this embodiment. Theequivalent electrical circuit would be similar to FIG. 15B except thatthe value C_(EFF2) is likely substantially smaller due to the thicknessof the support substrate. For example, a support substrate made ofsapphire (ε_(r)˜10) of 500 μm in thickness, C′_(EFF2) will beapproximately 18 pF/cm², about 65 times smaller than C_(EFF1). A fastervoltage ramp and/or a larger voltage value for V₁ could compensate forthis loss of coupling efficiency. For example, field plate voltagesource 1607 could be driven from 0 to +300V while the support substratevoltage source 1604 could be driven at 0 to −19.5 kV (−300V×65=−19.5kV). The electric field strength within the sapphire support substratewould be 0.4 MV/cm, below the dielectric breakdown strength of sapphire.If the selected bias conditions cause the electric field strength withinany of the dielectric regions approach or exceed safe operatingconditions needed to avoid dielectric breakdown, the material or biasconditions must be modified. Driven in this fashion, the LED deviceswould be driven substantially equivalently and allow C²I functional testwithout a buried contact within the LED device support substrate.High-voltage waveform generators to drive electrode 1603 can be realizedusing IGBT, MOSFET, or thyristor devices. High-voltage switches capableof switching up to 36 kV are model number HTS-361-01-C (36 kV, 12 A maxcurrent) and model number HTS-361-200-FI (36 kV, 2000 A max current)from Belke Electronic GMBH (Kronberg, Germany). Programmable waveformshaping circuits could slow the fast voltage change to a voltage rampmeeting the desired C²I functional test properties. For a 6″ substrate,the total capacitance would be about 3.2 nF and at 16 measurements perseconds, the ½ CV²f power would be about 10 Watts and the averagecurrent would be about 500 μA, safely within normal operatingspecifications for commercially available high-voltage switches. For theHTS-361-200-FI 2000 A capable switch, current density C²I measurementsas high as 11 A/cm² could be performed. Of course, there can be othervariations, modifications, and alternatives.

FIG. 17 shows capacitive current injection variants A, B and C which mayinclude up to 3 voltage sources to energize LED structure 1700. VariantA is a vertical LED structure where the top LED structure areacorresponds to the top electrode (anode) and the bottom LED structurearea corresponds to the bottom electrode (cathode). C_(top-a) istherefore equal to C_(EFF1) and C_(bot) is equal to C_(EFF2) of FIG.15B. Lateral LED structures such as the LED device 1701 with a small toparea etched to expose the n-layer 1702 (cathode) while the balance ofthe area contains the active layer, top p-layer and p-layer contact 1703(anode). In variant B, the top anode contact is accessible by aneffective capacitance C_(top-b) while cathode contact area 1702 isaccessible by an effective capacitance C_(bot-b). The cathode area isalso accessible through the support substrate 1704 via capacitanceC_(bot) and bottom electrode 1705. If the LED device has a total topsurface area equivalent to the variant A, C_(top-b)+C_(bot-b) will equalC_(top-a) and each capacitance value will be proportional to its surfacearea. For example, if the top anode area is 75% of the total area (andthe top cathode area is 25% of the total area), C_(top-b)=0.75×C_(top-a)and C_(bot-b)=0.25×C_(top-a). There is no change in C_(bot) since thetotal bottom area is not modified, however, the active area is smaller(75% in this example) due to the MESA etch contacting method. Effectivecurrent density injection value calculations would require active areato total area ratio correction. Variant C has a smaller top cathodecontact using a via contact. Except for differing capacitances andactive area to total area ratio values, variant C is similar to variantB.

Using the lateral LED MESA structure of variant B as an example LEDstructure, FIG. 18 shows a test assembly 1800 with three possiblecontacting options of three separate LED devices 1801 using a top fieldplate 1802 atop of the devices on the support substrate 1803 with abottom electrode 1804. Note that electrode 1804 can be an electrodeassembly including an overlying dielectric and may be placed inproximity to support substrate 1803. C_(bot) would be modified toinclude such additional dielectric layer(s) and gap.

Variant A of FIG. 18 has the top field plate electrode 1805 covering thecomplete LED device and driven with a voltage ramp to voltage V₁. Thebottom electrode 1804 is driven by a negative voltage ramp to voltageV₂. The top field plate electrode 1805 is assumed to be driven using apositive slope according to Phase I of FIG. 6A while the bottomelectrode 1804 is assumed to be driven by a negative slope where V₂ isscaled appropriately by the capacitances as explained further below.Variant B has a patterned field plate electrode where only an anodeelectrode 1806 is present and injects current into the LED devicethrough capacitance C_(t-b). The top cathode capacitance is assumed tobe negligible due to the absence of an electrode above the top cathodecontact area. Variant C has a patterned field plate electrode structurewhere the top anode contact is capacitively coupled to field plateelectrode 1807 using a positive ramp to voltage V₁ and the top cathodecontact is capacitively coupled to field plate electrode 1808 using anegative ramp to voltage V₃.

In yet another embodiment, Variant C of FIG. 18 can inject current indevice 1801 below top plate electrodes 1807 and 1808 in a capacitivemode and/or a DC mode without requiring bottom electrode 1804. In an AC(capacitive coupling) mode, the current would be developed usingtime-varying voltage waveforms impressed across electrodes 1807 and 1808to capacitively couple a displacement current within the LED device. InDC mode, the device would be energized by a current impressed by avoltage developed across electrodes 1807 and 1808 and an interfaceregion that can has a selected resistivity.

In a DC bias mode, FIG. 18 variant C electrodes develop a voltagegradient along the interface region between electrodes 1807 and 1808.This is a lateral gradient that can be used to bias multiple LED devicesif a sufficiently high differential electrode voltage is impressed. Forexample, if electrode 1807 was removed and a DC bias was developedacross electrodes 1806 and 1808, a roughly linear lateral voltagegradient would be developed across the LED devices of variant B and C.To turn on each of the LED devices using this lateral bias mode, eachLED device would require a minimum device threshold voltagedifferential. Assuming 3V for a GaN LED device and 50 μm LED devicecontact spacing, a voltage gradient of roughly 60 V/mm would be requiredacross the LED device lateral contacts. For multiple device lateralbiasing, the actual gradient would be somewhat higher due to devicestructure and spacing. This mode can be used to bias a string of LEDdevices such as in FIG. 18. Using a 200 device string of LED devices anda 50 μm device pitch, the bias voltage would be about 60 V/mm×200devices×0.05 mm or 600V. This bias applied across 10 mm would develop avoltage gradient of sufficient intensity to energize each of the 200 LEDdevices. This lateral bias mode could be used in conjunction withvertical capacitive bias to functionally test the LED devices on asubstrate. If the LED devices are alternating in polarity or a lower LEDdevice count is desired, a suitable patterned top field plate electrodestructure could be fabricated that can bias each LED deviceappropriately. Of course, there can be other variations, modifications,and alternatives.

Unless stated otherwise, zero net charge accumulation in the device(anode charge in=cathode charge out) and equal voltage ramp periods areassumed. Applying these bias conditions to the structures of FIG. 18 forphase I, the various relationships are as follows:

1. Variant A (lateral LED device, continuous field plate)

Injected current=C _(t-a) ×dV ₁ /dt

V ₂ =−V ₁×(C _(t-a) +C _(b-a))/C _(bot)

2. Variant B (lateral LED device, field plate electrode on anode only)

Injected current=C _(t-b) ×dV ₁ /dt

V ₂ =−V ₁ ×C _(t-b) /C _(bot)

3. Variant C (lateral LED device, separate field plate electrode onanode and cathode)

Injected current=C _(t-c) ×dV ₁ /dt

V ₁ ×C _(t-c) =−V ₂ ×C _(bot) −V ₃ ×C _(b-c)

For all three structures, J_(LED)=Injected current/active area, wherethe active area is the area of the MQW structure contacted by thedevice.

As merely examples to demonstrate the use of C²I measurement on lateraldevice structures, the LED structures of variants A-C of FIG. 18 areassumed with the following common parameters and photo-collectionconfiguration:

-   -   a. 25 μm×50 μm device size    -   b. 75% (anode & active area) and 25% (cathode) area split for        the lateral LED Device    -   c. Target J_(LED)=0.01 A/cm²    -   d. Sapphire support substrate thickness of 1 mm (ε_(r)=10)    -   e. Phase I voltage ramp time of 25 μsec    -   f. Field plate dielectric: 2 μm silicon nitride (ε_(r)=7.5)    -   g. C_(t-a)=C_(t-b)=C_(t-c)=31 fF    -   h. C_(b-a)=C_(b-c)=10.3 fF    -   i. C_(bot)=0.11 fF    -   j. Injected current=93.7 nA    -   k. E_(opt)=75 nJ/cm²    -   l. Photons/LED device emitted ˜1.5×10⁶ photons    -   m. Photo-electrons detected per LED device (65% quantum        efficiency, 90 mm lens aperture, 175 mm working distance)        ˜16,000 photo-electrons per C²I measurement cycle

Variant A Example 1:

-   -   a. V₁=+75V    -   b. V₂=−28.2 kV

Variant A Example 2 (Top Field Plate Grounded Condition):

-   -   a. V₁=0V    -   b. V₂=−28.275 kV

Variant B Example 1:

-   -   a. V₁=+75V    -   b. V₂=−21.3 kV

Variant B Example 2 (Top Field Plate Grounded Condition):

-   -   a. V₁=0V    -   b. V₂=−21.375 kV

Variant C Example 1:

-   -   a. V₁=+75V    -   b. V₃=−75V, V₂=−14.1 kV

Variant C Example 2:

-   -   a. V₁=+75V    -   b. V₃=−226V, V₂=0V

Although some common-mode charging will occur and higher bottomelectrode voltage V₂ may be required when example 2 of variant A of FIG.18 is used, this embodiment can be particularly useful by only requiringa grounded, nonpatterned field plate for most lateral LED structures.

In yet another embodiment, the top field plate can have a thickerdielectric and require a higher voltage V₁. This may have advantages inlessening top device structure topology effects, facilitate non-contacttesting and improve the robustness of the top field plate from slightdielectric imperfections such as scratches and the like. For example, a200 μm quartz field plate dielectric (element (f) in the previousexample) and a 10 um air gap would require the following voltages forvariant A of FIG. 18:

-   -   a. V₁=+17.4 kV    -   b. V₂=−28.5 kV        These voltages were chosen to avoid net charge transfer to the        devices, essentially keeping the LED device structure close to        ground potential. It is important to recognize that an air gap        will breakdown and become ionized if the electric field strength        is high enough. According to Paschen's Law for air at standard        pressure and temperature, a 10 μm air gap will breakdown at        about 350V while the above example assumed over 2.8 kV could be        maintained across the air gap. Instead, for V₁ voltages        exceeding about +2.2 kV in this example, the air gap will become        ionized and lower the voltage drop across the air gap. The        required V₁ will therefore be closer to +14.5 kV assuming no        voltage drop across the ionized air gap. Of course, other        voltage waveforms and values are possible to achieve the desired        current injection conditions. Of course, there can be other        variations, modifications, and alternatives.

When using a patterned field plate electrode pattern such as in variantsB and C of FIG. 18, a specific electrode pattern would be required forevery lateral device structure and the top field plate dielectricthickness must be less than or of the same order as the device pitch toavoid excessive electric field cross-coupling. Moreover, accuratepositional registration of a patterned top field plate between the fieldplate 1802 and the support substrate is important to maximize couplingefficiency and minimize parasitic capacitances (for example betweenelectrode 1807 and the n-layer cathode contact area). Positionalregistration between the electrode and the LED structure within +1-5% ofthe device size is believed to be adequate to allow efficient couplingand reproducible C²I measurement. For multiple electrode structures,such as variant C of FIG. 18, registration is also important to avoiddamaging the devices under test. For example, mis-registering the fieldplate to the device structures could negate current injection or evendamage the LED devices by injecting substantial reverse bias voltages.

In yet another example, the LED device can be equivalently biased withthe top field plate dielectric consisting of a 10 um DI water layer andthe bottom electrode is a buried electrode structure of 2 μm silicondioxide. This bottom structure is similar to FIG. 15A elements 1504 and1505. For this example, the requisite voltage ramp levels to develop theequivalent LED bias is:

-   -   a. V₁=+35V    -   b. V₂=−145V

In the preceding examples, a lateral device with a 75% MESA structurewas used. When using a vertical LED structure such as depicted invariant A of FIG. 17, the effective emission area is about 100% howeversome modifications to the device to confine current or manage leakageeffects on the perimeter may lower this effective area to less than100%. Assuming a 100% anode active area vertical structure, theequations and bias conditions can be calculated by settingC_(top-a)=C_(top)=C_(bot) and C_(bot-b)=0.

In the preceding equations, the light generation is assumed to occurinstantaneously and concurrently with the injected current. In a realLED device, a finite junction capacitance exists that requires charge tobias the device from a first state to the forward voltage state V_(F)before light emission starts occurring. This junction capacitance is afunction of the LED potential but for most GaN-based MQW structures, thejunction capacitance C′_(jct) is on the order of 60-200 nF/cm². Assuminga constant junction capacitance of 100 nF/cm², a zero-volt initial stateand a minimum forward voltage V_(F) of 2.5V, a net charge Q′_(jct) of250 nC/cm² must be supplied to the LED structure before light outputcommences. This introduces a charge offset that can limit the lowercharge injection limit of the C²I method. Equation 8 can be modified toaccount for this electrical charging effect (per unit area) as:

E′ _(opt)=η_(EXT)×(C′ _(EFF) ×ΔV−C′ _(inj) ×V′)×V _(F)   (10)

Where V′ is the effective voltage value required to charge the LED tothe emission threshold. This value can be zero if the LED is fullyprecharged to V_(F) if the LED is fully discharged to 0V.

-   Unless the LED is precharged to V_(F) in some manner before the    charge injection event occurs, the requirement to have the LED    charged to a level close to V_(F) before emission starts occurring    places a minimum ΔV condition as:

ΔV _(min)=(C′ _(inj) ×V _(F))/C′ _(EFF)   (11)

Assuming a zero-bias initial state, there will be little to no lightemission for voltage changes less than ΔV_(min).

This invention includes an ability to precharge the LED devices in amanner that can lower or even eliminate ΔV_(min) by using an externallight source to photo-electrically induce an open-circuit voltage on theorder of V_(F). An external light source meeting certain characteristicscan excite carriers to charge the LED device just before the chargeinjection event. The characteristics are:

-   -   1. Light having a wavelength less than or about the emission        wavelength of the LED device in order to efficiently excite        carriers across the bandgap.    -   2. Light of sufficient intensity to allow charging within an        acceptable time period and overcome recombination processes.        This effect can be modeled by writing the photodiode equation        for the LED device as follows:

I _(LED) =I _(o)×(e ^(qV/kT)−1)−I _(ph)   (12)

-   Where-   I_(LED)=Current flowing through the LED device (amperes)-   I_(o)=dark saturation current (amperes)-   V=LED voltage (volts)-   kT/q=Thermal voltage (about 25 mV at room temperature)-   I_(ph)=Photo-electrically induced current (amperes)

The light induced photocurrent I_(ph) is the quantity that an externallight source can generate. The level is roughly equal to theresponsivity in A/W (at a specific source wavelength) multiplied by theincident light power impinging on the LED MQW active layer in watts.

The LED voltage under open-circuit (I_(LED)=0) conditions can be derivedby rewriting equation 12 to solve for V_(LED):

V _(LED)(open-circuit)=kT/q×ln(I _(ph) /I _(o))   (13)

If I_(ph) is high enough, V_(LED) can approach V_(F) and thus can lowerΔV_(min) to a relatively small value. To prove this effect, a GaN-basedLED (Model 455D2 PCB mounted LED from Thorlabs, Inc., Newton, N.J. USA)having an emitting area of 1 mm², 455 nm emission wavelength andjunction capacitance of about 1.3 nF (measured at V=0) was used as atest LED. The LED, now operated and measured as a photodiode, wasilluminated using a similar GaN-based LED (Model 455L3 mounted LEDdriven from a Model LEDD1B LED driver, both from Thorlabs, Inc., Newton,N.J. USA) having an emission wavelength of 455 nm. The source LED wasdriven with 1000 mA of forward current. Irradiance at 200 mm distancewas specified at about 30 μW/mm². The measured I_(ph) (short-circuitcurrent condition) was about 5 μA and an open-circuit voltage V_(LED) ofabout 2.2V. This is close to the expected photocurrent of about 30μW/mm²×1 mm²×0.15 A/W=4.5 μA, where 0.15 A/W is an assumed responsivityfor this device based on similar devices and type. This confirms thepotential to use an external light source to precharge the LEDs tolevels close to V_(F) prior to the charge injection phase (Phase I) toreduce or eliminate ΔV_(min).

In a certain embodiment, the external light source would be activatedand used to precharge the LEDs under test but turned off just prior tothe start of the camera integration phase during Phase 1. This isdesirable if the light from this precharge phase light sourcesubstantially interferes with the LED emission measurement. For example,a 455 nm external light source to precharge LED devices also emitting at455 nm would add to the measurement to lower the measurement accuracyand possibly saturate the camera sensor. In this embodiment, the delaybetween the shutoff of the external light source to the Phase 1electrical voltage ramp start can lower the precharge state voltagethrough LED diode leakage current and other loss mechanisms such as lowLED light emission. While the shutoff time of the external light sourceused and the camera integration to electrical ramp time delays imposes alower limit to the delay time, keeping the precharge LED voltage staterelaxation to a minimum imposes an upper limit to the delay. In theexample above, the 455 nm LED light source required about 500 usec toturn off while an excessive precharge relaxation occurred after a fewmilliseconds of delay. FIG. 19

FIG. 19 shows a measured response of a test LED driven with a voltageramp after being illuminated with an external light source. The test LEDis a 455D2 PCB mounted LED driven by a voltage ramp of 3 μsec durationacross a 100 pF capacitor capable of withstanding the voltage waveformwithout breakdown. The optical measurement system consists of a camera(GS3-U3-23S6M-C from PointGrey Research Inc., Richmond, BC, Canada) witha 0.9× collection lens (#62-901 TECHSPEC™ large format telecentric lensmanufactured by Edmund Optics, Barrington, N.J., USA). The camera wasset with gain=0 dB, 500 μsec integration window and external triggering.The camera integration window was adjusted to minimize the residualexternal source effect on the camera response. The integration windowstart time was set at a set to 200 μsec delay from the external lightsource turn off and the pulse ramp start time was set to occur 300 μsecwithin the integration window. The external light source was a 455L3mounted LED driven from a LEDD1B LED driver, both from Thorlabs, Inc.,Newton, N.J. USA. The external light source was positioned about 200 mmfrom the test LED and driven with 1000 mA current. The expected externallight source flux impinging on the test LED is about 30 μW. The responsewith and without the external light source precharge shows a clearimprovement in the stored charge offset of equation 10. Decreasing theexternal light source to injection delay was shown to improve theemission offset, confirming that there is a relaxation of the LEDvoltage occurring between the turn-off of the external light source andthe LED current injection. FIG. 19 is a graph 1900 showing the result ofthe precharge effect with a 500 μsec external light source to injectiondelay. The horizontal scale is the voltage value V₁ in volts while thevertical scale is the measured ADU (Analog to Digital Units) count ofthe camera pixels receiving the imaged area within the test LED. Curve1900 is the measured response with no external light source photocurrentinjection. The response follows equation 10 and is linear to the voltageinjection levels with a voltage offset 1902 of approximately 80V. Thiscorresponds roughly to Q_(jct) of 80V×100 pF=8 nC. Referring to equation10 for a specific device of 1 mm² in area, this crossover would occur atC_(EFF)×ΔV=C_(inj)×V′=8 nC. Assuming V′=V_(F) of about 2.5V at theselower injection conditions, C_(inj) is about 3.2 nF or C′_(inj) about320 nF/cm². This higher than anticipated capacitance may be accounted bya higher junction capacitance process and the interconnect and wiringcapacitance of the specific test LED device used.

With the external light source enabled, the curve 1903 shows a clearreduction in the charge offset. Further reduction in timing delaybetween of the external light source and the LED current injection wouldallow the response to approach the zero-offset curve 1904.

Further optimization could include substituting a high-power LED lightsource with faster turnoff characteristic, faster light source drivercircuitry and lowering the camera integration start to electricalinjection onset delay. Of course, there can be other variations,modifications, and alternatives.

The external light source can greatly improve overall measurement systemthroughput by utilizing the injected photocurrent to safely decreasephase 3 discharge time. As a first example utilizing the test LEDconfiguration of FIG. 11, the minimum safe discharge time Δt wasestimated to be greater than about 60 msec assuming 10 μA/cm² or 10 pAfor a safe reverse bias leakage current. Using 30 μW/mm² illuminationand 0.15 A/W responsivity as an example, the effective leakage currentwould increase by 3 nW×0.15 A/W=450 pA. The minimum phase 3 dischargetime would be reduced to 1.3 msec. This would improve the capture framerate to more than 500 frames per second (FPS). Using the test LEDconfiguration of FIG. 19, the reverse leakage current was measured asabout 20 nA or 2 μA/cm². With a 100 pF coupling capacitor and 600Vinjection level, the dark minimum phase 3 discharge time would be about3 seconds or 0.33 FPS. Using the external illumination injecting about 5μA of photocurrent, phase 3 discharge time is now reduced to about 12msec, supporting a throughput measurement rate exceeding 80 FPS. Higherthroughput is possible by increasing the external light source fluxduring the phase 3 period. High-volume manufacturing requirements canthus be met with the use of this external light induced photocurrentinjection method. Of course, there can be other variations,modifications, and alternatives.

In yet another embodiment, the external light source would be selectedto emit light at a wavelength that can induce photocurrent in the LEDsunder test but at a sufficiently different wavelength from the LEDemission wavelength range to allow optical filtering to block theexternal light source emission from being substantially detected by themeasurement camera. A shorter wavelength source will tend to improveresponsivity by inducing photo-carriers within the test LED moreefficiently.

As an example, a 365 nm external light source (such as M365LP1-C1 fromThorlabs, Inc., Newton, N.J. USA) can be used to excite LED devices thatemit at longer wavelengths. For example, colored LED devices (red ˜620nm, green ˜520 nm, blue ˜460 nm) can be effectively filtered from theexternal light source using filters such as a UV-IR blocking filter anda color filter. For a green LED device test for example, a UV-IRblocking filter (model #89-802) and a green color filter (model #89-792)mounted on a compatible camera lens such as model #62901 0.9× largeformat telecentric lens is used, all available from Edmund Optics,Barrington, N.J., USA. FIGS. 20A and 20B show the optical transmissioncurves of these filters. FIG. 20A shows the transmission curve for theUV-IR blocking filter 2000 with the 365 nm external light source 2001and the LED device emission line 2002 centered around 520 nm. FIG. 20Bshows the transmission curve for the green bandpass filter 2003 with the365 nm external light source 2004 and the LED device emission line 2003centered around 520 nm. Each of the UV-IR blocking filter and the greenbandpass filter would add an optical density of about 4.5 for the 365 nmlight while allowing most of the LED device emission to pass. Thesefilters and perhaps others can be used singly or in a stackedconfiguration to optimize contrast and measurement performance. Ofcourse, there can be other variations, modifications, and alternatives.

Certain image processing methods can be utilized to improve the accuracyof the measured data corresponding to each LED device under test. Eachimaged LED device onto the sensor would be imaged onto a specific areawithin the camera sensor array. One image processing method uses spatialinformation from the target image to generate a physical centroid (x,y)location for each LED device within the measured camera output dataimage. This correspondence of LED device centroid location on thesupport substrate to its corresponding centroid location on the camerasensor can be developed and possibly corrected using cameramagnification, optical distortion correction, image capture to sense andlocate the LED device matrix and the like. The resulting centroid matrixwould therefore be the set of (x,y) location within the sensor image foreach LED device. For example, referring to the previous example, a960×600 LED device set imaged onto a 1920×1200 digital sensor matrixwould have a centroid matrix as follows:

Centroid for LED (i,j)=Camera data location (x.y)

Where i, j are integers (i=1 to 960, j=1 to 600) for each measured LEDwhile the camera location (x,y) is a floating point number within thesensor pixel area (0<x<1920, 0<y<1200). Once this centroid matrix isdeveloped, image processing methods using weighted functions can takethe digitized image and develop a set of data values that are extractedusing a weighing function where more weight is given to sensor dataimaged closest to the physical LED centroid location. Image processingsystems can accomplish this convolution function in parallel and usuallyat frame rate speeds. The LED data values thus comprises of an outputLED device (i,j) matrix of data values calculated using centroidweighted functions applied to the digitized camera data in a preferredembodiment.

While the above describes the key steps to C²I data image capture toyield an output LED device (i,j) data point, offset andscaling/normalization operations can also be applied. For example, a“dark” image captured without the voltage waveforms would measure thedark signal for each camera pixel at the current image acquisitionparameters. These dark images can be acquired along with each C²I datacapture as a form of offset and drift cancellation. The reference can besubtracted from the image data or after both data and reference havebeen processed using centroid weighted functions described above toyield an offset-corrected LED device (i,j) data matrix. Scaling andnormalization operations are also possible.

Additional image processing methods applied to the digitized cameraoutput (proportional to the total integrated light emitted by the LEDdevices imaged onto the camera sensor(s) during phase I) can be utilizedto develop a result indicative of LED device functionality. Thisfunctional data will be in the form of a matrix that contains one ormore values derived from the measurement. For each LED at location(i,j), there will be a set of n data points Data_(n)(ij)=Value_(n)(where n is an integer greater or equal to 1). Multiple independentData_(n)(ij) values for each LED under test for example, could be valuesof light output at differing current density values measured using nmeasurement sequences taken with different phase I voltage ramp values.Each Data_(n)(ij) measurement data value can in turn be the average ofmultiple measurements to improve signal-to-noise ratio. Signal averagingis a well-known method where the standard deviation of a signalexhibiting stochastic noise would be reduced by sqrt(m) where m is thenumber of measurements points that are averaged. For example, if a datapoint exhibiting a stochastic noise standard deviation of z, averageddata points using the average of 100 data points would have a standarddeviation of z/sqrt(100) or 10 times lower.

Once the LED device (i,j) data values are collected, a threshold or setof test criteria can be applied to develop a determination offunctionality, perhaps adding a Data_(n)(ij) value of 0 or 1 (0=baddevice, 1=good device) for each LED being measured. For example,non-emitting or weakly emitting devices could be labeled as bad devicesif a desired minimum threshold is applied to the data. Of course,multiple thresholds and other criteria applied to the set of data valuesor the pass/fail criteria could also be useful in functional test,repair strategies and process yield analysis (cause and correction). Asmerely an example, multiple thresholds could be applied to the LEDdevice Data_(n)(ij) data to generate a bin number label for each LEDdevice to match LEDs in functionality and drive a strategy of releasingdevices with similar characteristics according to a criteria or set ofcriteria. Random-access laser lift-off or other individual LED devicerelease methods could aggregate LED devices having similar bin numbersbased on the bin label matrix value for each (i,j) LED device. Thiscould be useful to limit display non-uniformity caused by using LEDdevices having excessively different functional characteristics.Multiple thresholds could also be utilized to develop statistics usefulfor yield and process control. For example, the standard deviation andother statistical analyses applied to bin data can be an indicator ofyield and process stability. Sudden changes in these derived quantitiescan signal a process excursion. FIG. 21 shows a histogram plot 2100 ofseveral LED devices falling within small ranges of Data_(n) values(called channels or bins) on the vertical scale as a function ofData_(n) in the horizontal scale. Most of the LED devices fall within afunctionally acceptable range 2101 while LED devices below threshold2102 or above threshold 2103 are considered rejects. The width 2104 ofthe LED device binning function can be useful for yield and processcontrol. LED devices falling within similar bins 2105 could be lateraggregated and used for their similar functional test results to improvedisplay uniformity.

If the functional test apparatus according to this invention images lessthan the desired area and requires a step and repeat function, thecentroid matrix may need to be recalculated for each new LED device areato be measured. If the step system is sufficiently accurate to align thenext set of LED devices to be measured however, the centroid matrix maybe reused. Of course, there can be other variations, modifications, andalternatives.

Generally, a field plate allows functional testing of a substratecontaining LED devices to occur either by one or more cameras fixed ormoved relative to the field plate. Test equipment cost, complexity,target LED device size and test throughput capability are some of thecriteria that must be evaluated before a specific configuration isselected. Other design limitations and criteria must also be addressedto assure measurement functionality to desired specifications. One suchdesign criteria is assuring the phase I voltage waveform across each LEDdevice being tested is not significantly distorted due to contactresistance and parasitic capacitance. For example, a fast voltage rampfor Phase I desired to measure higher current density operation couldcause a significant waveform distortion and voltage drop caused by RClow-pass filtering for LED devices situated in the middle of the fieldplate. This could occur if the field plate electrode or common contactresistance is too high. Mitigation of these effects could happen bylowering the effective contact sheet resistivity or attaching a lowerresistivity layer before testing. Finally, a large field plate willrequire power to charge & discharge the field plate capacitance C_(FP)at the measurement repetition rate and may generate resistive heatingwithin the contact layers. For example, a 6″ substrate field plate usinga 3 μm silicon dioxide dielectric layer would have a total capacitanceC_(FP) of about 200 nF. If a 16 Hz capture rate and 500V ramp isassumed, the ½ CV²f power would be about 0.5 W. At this proposedoperating point, small and manageable test power levels are generated,even with a full 6″ field plate configuration.

In yet other embodiments, an external light source can be used as amethod alone or in conjunction with C²I injection to excite the LEDdevices to measure emission levels in specific time periods controlledby the camera time integration window timing and width. For example,irradiation by an external light source blocked from detection by thecamera by spectral filtering means described earlier can be used tomeasure LED leakage, responsivity and emissivity with improved contrastand signal to noise ratio. For example, a leakage map of an LED arraycan be captured by scanning the camera integration window from prior tothe turnoff time of the external light source to a point later than theturnoff time of the external light source (for example, from 0 to 1msec). With a sufficiently high external light flux, residual emissionand decay characteristics by each LED under test can be measured as afunction of this delay. Defective LEDs usually exhibit significantnon-radiative leakage and other mechanisms that decrease LED lightemission. The resulting map can be used to generate a defect file of allmeasured LEDs to identify LEDs that have low abilities to emit lightafter being irradiated by the external light source. C²I methods can beadded to the external light source excitation to add an additional levelof injection that further increases the ability to functionally test theLEDs to determine functionality.

The signal processing use of offset cancellation (such as “dark image”subtraction) and the use of an external light source can be combined todevelop different modes of test. If a processed data is the subtractionof a second measurement “B” from a first measurement “A”, each imageprocessing data point in the data array would be (A-B) to form an offsetcorrected data array or image. If A is the functional image with thevoltage waveforms while the B is the image without the voltagewaveforms, the (A-B) functional image would be corrected for “darkimage” offsets. In this example, the current injection “EL” orelectroluminescent input is said to be in differential mode (DM). If thevoltage waveforms are present in both A and B images, the EL input issaid to be in “Common Mode” or CM. In CM mode, the data is essentiallysubtracted out and the (A-B) frame would be a null image. Similarly, ifthe external light source is present in the A image but not in the Bimage, the “PL” or photoluminescent light bias would be in differentialmode or DM mode. Finally, if the external light source input is presentin both A image and B images, the PL input would be said to be in commonmode or CM mode. Using this as a reference, EL and PL modes of operationcan be described as follows:

-   -   1. EL=DM, PL=No light: EL functional test without external light        source    -   2. EL=DM, PL=CM: EL functional test with common-mode external        light bias    -   3. EL=No voltage input, PL=DM: PL test    -   4. EL=DM, PL=DM: EL functional test with differential-mode        external light bias        The other possible modes are of limited use. For example, EL=CM,        PL=CM would result in a null result.

The measurement mode of PL test (3 above) and EL functional test with orwithout light bias (1, 2 or 4 above) can be measured in quick successionand yield useful information about the LED devices. If the externallight is used to bias the device as in FIG. 19, the corresponding ELfunctional test would be mode 2 (EL=DM, PL=CM) while a PL test would bemode 3 (EL=No voltage input, PL=DM). Of course, there can be othervariations, modifications, and alternatives.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Although the above has been described using a selected sequence ofsteps, any combination of any elements of steps described as well asothers may be used. Additionally, certain steps may be combined and/oreliminated depending upon the embodiment. Furthermore, although thedescription and examples has been directed towards GaN LED devices on aplanar surface, any planar or curved surface containing photon emittingdevices could be functionally tested using the C²I method. For example,Vertical-Cavity Surface-Emitting Lasers (VCSELs), Organic LEDs (OLEDs),silicon photonics devices and other surface emitting devices could betested using this invention. Additionally, in another example, II-VIsemiconductor materials and associated devices can also be used. Ofcourse, there can be other variations, modifications, and alternatives.Therefore, the above description and illustrations should not be takenas limiting the scope of the present invention which is defined by theappended claims.

What is claimed is:
 1. An apparatus for observing light emission from alight-emitting device structure disposed on a support substrate having afirst contact layer accessible from a surface and a second contact layerincluded on the light-emitting device structure, the light emittingdevice structure being selected from either a vertical light emittingdevice structure or a lateral light emitting device structure, theapparatus comprising: a field plate device, the field plate devicehaving a first face and a second face opposing the first face, thesecond face comprising a conductive layer, the conductive layer being inclose proximity to at least a portion of the first contact layer of thelight-emitting device structure with an intervening interface region; avoltage source for producing a voltage, the voltage source being capableof generating a time-varying voltage waveform, the voltage source havinga first terminal and a second terminal, the first terminal having afirst potential coupled to the conductive layer of the field platedevice, the second terminal at a second potential, the voltage sourcebeing capable of injecting a capacitively coupled current to the lightemitting device structure to cause at least a portion of thelight-emitting device structure to emit electromagnetic radiation in apattern; and a detector device coupled to the light emitting devicestructure to form an image of the electromagnetic radiation in thepattern derived from the light-emitting device structure.
 2. Theapparatus of claim 1 wherein the second terminal is electrically coupledto the backside of the support substrate, the second potential being atground potential or at negative potential or positive potential inrelation to the ground potential to create the time-varying voltagewaveform.
 3. The apparatus of claim 1 wherein the first terminal iselectrically connected to the conductive layer of the field plate deviceand being at a ground potential or at a negative potential or a positivepotential in relation to the ground potential to create the firstpotential.
 4. The apparatus of claim 1, wherein the interface layer is agap medium.
 5. The apparatus of claim 4, wherein the gap mediumcomprises a gas or vacuum.
 6. The apparatus of claim 4, wherein the gapmedium comprises a liquid.
 7. The apparatus of claim 6, wherein theliquid is selected from the group consisting of water, deionized water,alcohol, methanol, and ethylene glycol.
 8. The apparatus of claim 1,wherein the interface layer comprises a dielectric layer and a gapmedium.
 9. The apparatus of claim 8, wherein the gap medium comprises agas or vacuum.
 10. The apparatus of claim 8, wherein the gap mediumcomprises a liquid.
 11. The apparatus of claim 10, wherein the liquid isselected from the group consisting of water, deionized water, alcohol,methanol, and ethylene glycol.
 12. The apparatus of claim 8, wherein thedielectric layer is a layer present between the conductive layer and thegap medium selected from the group consisting of silicon dioxide,silicon nitride, alumina (Al2O3), glass, quartz, and plastic.
 13. Theapparatus according to claim 1 wherein the lateral light emitting devicestructure comprises a first contact layer and a second contact layer,the first contact layer and the second contact layer being electricallyaccessible on at least one face of the lateral light emitting devicestructure.
 14. The apparatus according to claim 1 wherein the image isderived from a light output of an emitting surface of the light emittingdiode structure resulting from application of a capacitively coupledtime varying voltage waveform.
 15. The apparatus according to claim 3wherein the conductive layer is patterned and comprises a first portionwithin a vicinity of the first contact layer and a second portion withina vicinity of the second contact layer, the first portion beingelectrically and physically separated from the second portion the firstportion being connected to the first terminal of the voltage source, andthe second portion being connected to another voltage source or a groundpotential.
 16. The apparatus according to claim 3 wherein the conductivelayer comprises a first portion within a vicinity of the first contactlayer and an absence of a conductive layer within a vicinity of thesecond contact layer.
 17. The apparatus according to claim 1 wherein thevertical light emitting device structure comprises the first contactlayer and the second contact layer underlying the light emitting devicestructure.
 18. The apparatus according to claim 1 further comprising alens coupled to the detector device for focusing the electromagneticradiation provided on the detector device.
 19. The apparatus accordingto claim 1 wherein the field plate device is transmissive to theelectromagnetic radiation and the electromagnetic radiation passesthrough the field plate device.
 20. The apparatus according to claim 1wherein the support substrate is transmissive to the electromagneticradiation and the electromagnetic radiation passes through the supportsubstrate.
 21. The apparatus according to claim 1 wherein the detectordevice comprises imaging the electromagnetic radiation to produce anobservable map of the pattern of electromagnetic radiation as a functionof position over the light-emitting device structure of the supportsubstrate.
 22. The apparatus according to claim 1 wherein detectordevice comprises a camera; and further comprising an electrical accesscoupled to the second contact layer of the light-emitting devicestructure using an electrical contact or using capacitive coupling. 23.The apparatus according to claim 22 wherein the field plate device istransmissive and the camera is mounted to image the light-emittingdevice structure to collect the electromagnetic radiation through thefield plate device.
 24. The apparatus according to claim 22 wherein thesupport substrate is transmissive and the camera is mounted to image thelight-emitting device structure to collect the electromagnetic radiationthrough the support substrate.
 25. The apparatus according to claim 1wherein the time-varying voltage waveform is a voltage ramp from a firstvoltage potential to a second voltage potential to forward bias thelight-emitting device structure at selected current density during themeasurement phase.
 26. The apparatus according to claim 22 wherein thecamera integrates the electromagnetic radiation over the time-varyingvoltage waveform to produce a spatial map of total electromagneticradiation produced over the light-emitting device structure.
 27. Theapparatus according to claim 26 wherein the spatial map of integratedelectromagnetic radiation is processed using image processing device toperform one or more of the following functions: signal averaging,thresholding and binning to develop a spatially-dependent functionaltest result of the light-emitting device structure.
 28. The apparatusaccording to claim 1 wherein the first contact layer of thelight-emitting device structure is isolated using a material removalprocess to realize a plurality of individually addressablelight-emitting devices.
 29. The apparatus according to claim 1 whereinthe first and second contact layers of the light-emitting devicestructure are isolated using a material removal process to realize aplurality of individually addressable light-emitting devices.
 30. Theapparatus according to claim 25 wherein the time-varying voltagewaveform after the measurement phase is returned from the second voltagepotential to the first voltage potential over a time period called thereset phase selected to use the light-emitting device reverse biasleakage current density and avoid exceeding potentially damaging reversebias voltage.
 31. The apparatus according to claim 1 wherein an externallight source is used to irradiate the light-emitting device structure toinduce a photocurrent.
 32. The apparatus according to claim 31 whereinthe external light source wavelength is shorter than the emissionwavelength of the light-emitting device structure.
 33. The apparatusaccording to claim 31 wherein the photocurrent forward biases thelight-emitting device structure prior to the time-varying voltagewaveform.
 34. The apparatus according to claim 31 wherein thephotocurrent increases the leakage current of the light-emitting devicestructure after the measurement phase to reduce the reset phase timeperiod.
 35. The apparatus according to claim 1 wherein spectralfiltering consisting of blocking filters are interposed between thedetector device and the light-emitting device structure to blockunwanted light and pass the light emitted from the light-emitting devicestructure.
 36. The apparatus according to claim 35 wherein the detectorhas a light integration time start and duration; wherein thelight-emitting device structure emission efficiency is measured at aspecific time window with respect to modulation of external light sourceirradiation.
 37. The apparatus according to claim 35 wherein atime-varying voltage waveform is combined with external lightirradiation to determine light-emitting device structure functionality.38. The apparatus according to claim 22 wherein the camera is one of aplurality of cameras, each positioned to image a separate area of thelight-emitting device structure.
 39. The apparatus according to claim 22wherein the camera and a smaller field plate device is an assembly thatcan image a smaller test area and mechanically indexed in a step andrepeat fashion for more complete test coverage.
 40. The apparatusaccording to claim 1 wherein the field plate device is approximately thesame areal dimension to the support substrate and is placed on thesupport substrate to allow substantially complete functional testing ofthe support substrate without step and repeat indexing of the fieldplate device.
 41. The apparatus according to claim 1 wherein the fieldplate is placed in close proximity to the support substrate using a sealnear the periphery of the field plate and air is evacuated from the gapusing a vacuum port.
 42. The apparatus according to claim 1 wherein thefield plate is placed in close proximity to the support substrate usinga seal near the periphery of the field plate and a liquid is introducedinto the gap using fill input and output ports.
 43. The apparatusaccording to claim 1 wherein the close proximity between the field plateand the support substrate device is actual contact.
 44. A method ofmanufacturing an optical device, the method comprising: providing alight emitting diode structure, the light emitting diode structurehaving a plurality of LED devices to be formed, disposed on a supportsubstrate having a first contact layer accessible from a surface and asecond contact layer provided on the light-emitting device structure,the light emitting diode structure being either a vertical lightemitting diode structure or a lateral light emitting diode structure;coupling a field plate device to the light emitting diode structure, thefield plate device having a first face and a second face opposing thefirst face, the second face comprising a conductive layer, theconductive layer being in close proximity to at least a portion of thefirst contact layer of the light-emitting device structure with anintervening interface region; generating a time-varying voltage waveformfrom a voltage source to form a voltage potential between the dielectriclayer of the field plate device and the light emitting device structureto inject current to at least a plurality of the LED devices in thelight emitting device structure to cause the light-emitting devicestructure to emit electromagnetic radiation in a pattern; and capturing,using a detector device coupled to the light emitting device structure,an image of the electromagnetic radiation in the pattern derived fromthe light-emitting device structure.
 45. The method according to claim44 wherein the field plate device is transmissive to the electromagneticradiation and the electromagnetic radiation passes through the fieldplate device.
 46. The method according to claim 44 wherein the surfaceof a support substrate is transmissive to the electromagnetic radiationand the electromagnetic radiation passes through the support substrate.47. The method according to claim 44 wherein the detector devicecomprises imaging the electromagnetic radiation to produce an observablemap of the pattern of electromagnetic radiation as a function ofposition over the light-emitting device structure of the supportsubstrate.
 48. The method according to claim 47 wherein detector devicecomprises a camera.
 49. The method according to claim 47 wherein thefield plate device is transmissive and the camera is mounted to imagethe light-emitting device structure to collect the electromagneticradiation through the field plate device.
 50. The method according toclaim 47 wherein the support substrate is transmissive and the camera ismounted to image the light-emitting device structure to collect theelectromagnetic radiation through the support substrate.
 51. The methodaccording to claim 44 wherein the time-varying voltage waveform is avoltage ramp from a first voltage potential to a second voltagepotential to forward bias the light-emitting device structure atselected current density during the measurement phase.
 52. The apparatusaccording to claim 47 wherein the camera integrates the electromagneticradiation over the time-varying voltage waveform to produce a spatialmap of total electromagnetic radiation produced over the light-emittingdevice structure.
 53. The apparatus according to claim 52 wherein thespatial map of integrated electromagnetic radiation is processed usingimage processing device to perform one or more of the followingfunctions: signal averaging, thresholding and binning to develop aspatially-dependent functional test result of the light-emitting devicestructure.
 54. The method according to claim 44 wherein the time-varyingvoltage waveform after the measurement phase is returned from the secondvoltage potential to the first voltage potential selected to use thelight-emitting device reverse bias leakage current density and avoidexceeding potentially damaging reverse bias voltage.
 55. The methodaccording to claim 44 where an external light source is used to induce aphotocurrent within the light-emitting device structure to decrease timeperiod to return the time-varying voltage waveform from the secondvoltage potential to the first voltage potential and avoid exceedingpotentially damaging reverse bias voltage.
 56. The apparatus accordingto claim 55 wherein the photocurrent forward biases the light-emittingdevice structure prior to application of the time-varying voltagewaveform.
 57. The method according to claim 44 wherein the first contactlayer of the light-emitting device structure is isolated using amaterial removal process to realize a plurality of individuallyaddressable light-emitting devices.
 58. The method of claim 44 whereinthe first and second contact layers of the light-emitting devicestructure are isolated using a material removal process to realize aplurality of individually addressable light-emitting devices.
 59. Amethod of manufacturing an optical device, the method comprising:providing a light emitting diode structure, the light emitting diodestructure disposed on a support substrate having a first face contactlayer accessible from a surface and a second contact layer underlyingthe light-emitting device structure; coupling a field plate device tothe light emitting diode structure, the field plate device having afirst face and a second face opposing the first face, the second facecomprising a conductive layer, the conductive layer being in closeproximity to at least a portion of the first contact layer of thelight-emitting device structure with an intervening interface region;generating a time-varying voltage waveform from a voltage source to forma voltage potential between the dielectric layer of the field platedevice and the light emitting device structure to inject current to aplurality of the LED devices in the light emitting device structure tocause the light-emitting device structure to emit electromagneticradiation in a pattern; and capturing, using a detector device coupledto the light emitting device structure, an image of the electromagneticradiation in the pattern derived from the light-emitting devicestructure.
 60. The method according to claim 59 wherein the field platedevice is transmissive to the electromagnetic radiation and theelectromagnetic radiation passes through the field plate device.
 61. Themethod according to claim 59 wherein the surface of a substrate undertest is transmissive to the electromagnetic radiation and theelectromagnetic radiation passes through the support substrate.
 62. Themethod according to claim 59 wherein the detector device comprisesimaging the electromagnetic radiation to produce an observable map ofthe pattern of electromagnetic radiation as a function of position overthe light-emitting device structure of the support substrate.
 63. Themethod according to claim 62 wherein detector device comprises a camera.64. The method according to claim 63 wherein the field plate device istransmissive and the camera is mounted to image the light-emittingdevice structure to collect the electromagnetic radiation through thefield plate device.
 65. The method according to claim 63 wherein thesupport substrate is transmissive and the camera is mounted to image thelight-emitting device structure to collect the electromagnetic radiationthrough the support substrate.
 66. The method according to claim 59wherein the time-varying voltage waveform is a voltage ramp from a firstvoltage potential to a second voltage potential to forward bias thelight-emitting device structure at a selected current density during themeasurement phase.
 67. The method according to claim 59 wherein thetime-varying voltage waveform after the measurement phase is returnedfrom the second voltage potential to the first voltage potentialselected to use the light-emitting device reverse bias leakage currentdensity and avoid exceeding potentially damaging reverse bias voltage.68. The method according to claim 59 where an external light source isused to induce a photocurrent within the light-emitting device structureto decrease time period to return the time-varying voltage waveform fromthe second voltage potential to the first voltage potential and avoidexceeding potentially damaging reverse bias voltage.
 69. The apparatusaccording to claim 68 wherein the photocurrent forward biases thelight-emitting device structure prior to application of the time-varyingvoltage waveform.
 70. The apparatus according to claim 63 wherein thecamera integrates the electromagnetic radiation over the time-varyingvoltage waveform to produce a spatial map of total electromagneticradiation produced over the light-emitting device structure.
 71. Theapparatus according to claim 70 wherein the spatial map of integratedelectromagnetic radiation is processed using image processing device toperform one or more of the following functions: signal averaging,thresholding and binning to develop a spatially-dependent functionaltest result of the light-emitting device structure.
 72. The methodaccording to claim 59 wherein the first contact layer of thelight-emitting device structure is isolated using a material removalprocess to realize a plurality of individually addressablelight-emitting devices.
 73. The method according to claim 59 wherein thefirst and second contact layers of the light-emitting device structureare isolated using a material removal process to realize a plurality ofindividually addressable light-emitting devices.
 74. A method ofmanufacturing an optical device, the method comprising: providing alight emitting diode structure overlying a substrate member, the lightemitting diode structure disposed on a support substrate having a firstface contact layer accessible from a surface and a second contact layerunderlying the light-emitting device structure; coupling a field platedevice to the light emitting diode structure, the field plate devicehaving a first face and a second face opposing the first face, thesecond face comprising a conductive layer, the conductive layer being inclose proximity to at least a portion of the first contact layer of thelight-emitting device structure with an intervening interface region;generating a time-varying voltage waveform from a voltage source to forma voltage potential between the dielectric layer of the field platedevice and the light emitting device structure to inject current to aplurality of the LED devices in the light emitting device structure tocause the light-emitting device structure to emit electromagneticradiation in a pattern; and capturing, using a detector device coupledto the light emitting device structure, an image of the electromagneticradiation in the pattern derived from the light-emitting devicestructure; processing light emitting device structure overlying thesubstrate to either singulate the light emitting device structure orperform another process on the light emitting device structure; couplingat least a pair of interconnect members to the light emitting devicestructure; and integrating the light emitting device structure into anapplication, the application being selected from a general lightingdevice, a luminaire, a display, a projector, a lamp for a vehicle, or abeam light, or a specialty lighting device.
 75. The method of claim 74wherein the LED devices in the light emitting device structure are freefrom a probe mark or other test mark.